It is known to cover all or part of a steering mechanism, and in particular the gear transmission elements of such a mechanism, by a rigid casing which ensures guiding, protecting and/or maintaining in a lubricant said mechanism.
In order to enable the setting-up or the maintenance of the mechanism, for example draining or filling the lubricant, the casing is provided with one or several access orifice(s), which of course must be closed, in normal operation, so as to guarantee sealing of the casing.
To this end, threaded plugs, intended to be screwed in threaded ends of the access orifices, are generally used, or still further cowls provided with a plurality of peripheral fastening legs which are clamped by screws on the casing, in order to hide the considered orifices.
In either case, sealing is generally ensured by a seal, such as an O-ring seal, which is compressed by the plug or the cowl against the rim of the orifice.
However, this kind of closure is generally satisfactory from the functional point of view, but it may nonetheless present some drawbacks.
Indeed, multiplying the parts required for the closure (complex-shaped plug, seal, screw . . . ) tends to complicate the assembly of the casing, and to increase its manufacturing cost, as well as its weight and its overall dimension.
Furthermore, it is generally difficult to check, in particular visually, the proper setting of the closure elements, and in particular the positioning of the seal, so that sealing defects may sometimes occur or subsist without being detected immediately, which may be detrimental to the proper operation and to the longevity of the steering system.